Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $48.74   13.243%   $55.1946   $55.19   $55.20   $55.20  
  Purchase #2 $136.75   9.142%   $149.2517   $149.25   $149.25   $149.30  
  Purchase #3 $237.48   6.675%   $253.3318   $253.33   $253.35   $253.30  
  Purchase #4 $48.69   10.170%   $53.6418   $53.64   $53.65   $53.60  
  Purchase #5 $181.50   8.307%   $196.5772   $196.58   $196.60   $196.60  
  Purchase #6 $235.25   11.605%   $262.5508   $262.55   $262.55   $262.60  
  Purchase #7 $109.70   9.746%   $120.3914   $120.39   $120.40   $120.40  
  7 purchase totals = $998.11       $1,090.9393   $1,090.93   $1,091.00   $1,091.00